1. Field of Invention
The present invention relates to a locking apparatus for a parking brake. More particularly, the present invention relates to a locking apparatus for a parking brake which may maintain locking state even electric power is not applied.
2. Description of Related Art
Generally, a parking apparatus (parking brake), which maintains a vehicle in stop state by locking a sprag disposed to an output shaft with a parking gear at parking range “P”, is provided to an automatic transmission.
FIG. 4 is a cross-sectional view of a conventional parking brake.
A conventional parking apparatus includes a detent lever 12 which is connected to a shift lever 10 and rotates according to the shift lever 10 selecting parking mode, a parking rod 14 which is connected to the detent lever 12 and moves rectilinearly by rotating of the detent lever 12 and of which a roller 28 is disposed to an end thereof, a sprag 18 which is rotatable around a hinge 30 and of which a locking protrusion 34 is formed to an end thereof, a return spring 32 which is disposed to the hinge 30 for supplying a restoring force to the sprag 18 and a parking gear 22 of which an engaging groove 20 selectively engaged with the locking protrusion 34 is formed thereto.
A rod spring 26 is disposed to the parking rod 14 for supplying a restoring force thereto.
In the conventional parking apparatus, when a driver manipulates the shift lever 10 to a parking mode, the detent lever 12 connected to the shift lever 10 rotates and then the parking rod 14 connected to the detent lever 12 moves rectilinearly. And then the roller 28 connected to an end of the parking rod 14 rotates the sprag 18.
And thus the parking gear 22 of the sprag 18 is engaged with the engaging groove 20 of the parking gear 22 for fixing the parking gear 22, so that parked state is maintained.
When the shift lever 10 is shifted from parking mode to other mode, the parking rod 14 cranks back by elastic force of the rod spring 26 and the sprag 18 also cranks back by elastic force of the return spring 32 and thus the locking protrusion 34 and the engaging groove 20 are separated so that parked state is finished.
Recently, a SBW (Shift By Wire) is usually used for transmitting driver's will to TCU so that mechanical parking is released by hydraulic pressure. So that just small power comparing to a conventional TGS (Transmission Gear Shift) lever (P/R/N/D) is required, and thus a driver is provided convenience.
Also, a solenoid valve and locking apparatus are used for preventing mechanical parking of a transmission when a vehicle is driven as a driving mode, for example D shift, and hydraulic pressure supplied to a parking piston is rapidly released.
However, in the conventional art, electric current must be supplied for maintaining locking state. And thus, if electric power in N shift is cut off, a brake is engaged.
With this scheme, a driver is provided with an inconvenience especially in a narrow parking area.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.